1. Field of the Invention
The present invention provides a system for rheologically evaluating a wide range of materials and, more specifically, it provides such a system which has positive means for effecting more efficient measurement of the rheological properties of the specimen.
2. Description Of The Prior Art
It has long been known that various proxies of certain materials can be measured effectively using rheometers.
U.S. Pat. No. 5,209,108 disloses a helical screw rheometer wherein a computer processes signals received from pressure sensing means and speed sensing means.
U.S. Pat. No. 5,269,190 discloses an axial rheometer wherein a microprocessor causes axial displacement of the sample holder to deform the sample.
U.S. Pat. No. 5,277,058 discloses an adjustable gap rheometer wherein the dimension between a stationary section and a movable section is altered to facilitate determination of shear rate and shear stress for varying deformation rates.
U.S. Pat. No. 5,315,863 discloses measurement of a fluid or a slurry in a continuous on-line measurement detecting rheological properties. An inverted U-tube is employed with pressures being compared at a point in each leg. U. S. Pat. No. 5,347,852 also discloses m on-line rheological measurement apparatus wherein a portion of the melt is diverted to a capillary passage by means of a first metering pump and is returned by means of a second metering pump.
It has been known to measure dynamic shear properties proxies employing a rheometer wherein a stationary plate and a rotatable plate are provided with a specimen therebetween. The rotatable plate is subjected to oscillating movement relative to the stationary plate. This system measures torque dung a predetermined angular rotation and employs a transducer and computer to calculate the rheological properties at different temperatures. See U.S. Pat. No. 5,357,783 and also the two surface oscillating plate of related U.S. Pat. No. 5,271,265.
U.S. Pat. No. 5,303,578 also discloses a dynamic rheometer. This patent discloses shear waves impinging on two spaced shear receiving surfaces with a transducer being provided for each surface.
U.S. Pat. No. 5,302,878 discloses a high-feed acoustic rheometer wherein a torsional-mode transducer in a cylinder interacts with a sensor in a rod with the respective diameters of the torsional-mode transducer and the sensor being such that the coefficient of reflection at the interface of the transducer-sensor is zero.
U.S. Pat. No. 5,167,143 discloses a rheometer having a motor driven chamber which is said to be usable for measuring fluids, slurries and finely divided particulated solids. An annular gap is provided between the motor driven chamber and spindle with an associated transducer being employed. The system is said to convert shear into viscosity.
U.S. Pat. No. 5,349,847 discloses a rotatable rheometer wherein the rotatable plate, specimen and stationary plate are adapted to be separated from the thick support which supports the stationary plate with magnetic means employed to effect retention. This is said to facilitate more efficient operation of the equipment which can be switched from operation in a rotational mode to operation in an oscillating mode.
In spite of this known system, there remains a very real and substantial need for an improved type of rotary rheometer which will effect more efficient interengagement between the specimen and the plates in order to provide more accurate results.